Update changelog for 2.1.5 and 2.2.4
Update changelog for 2.1.5 and 2.2.4

Kriechi/hyper-h2,Kriechi/hyper-h2,python-hyper/hyper-h2,vladmunteanu/hyper-h2,python-hyper/hyper-h2,vladmunteanu/hyper-h2,bhavishyagopesh/hyper-h2